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Fluenz: first intranasal influenza vaccine

Fluenz, a live attenuated vaccine, is licensed for influenza prophylaxis in children aged 2-18 years.

Fluenz is given as a 0.2ml dose (0.1ml per nostril), with a second dose after at least 4 weeks in children not previously vaccinated against influenza

PHARMACOLOGY

Fluenz is a live attenuated influenza vaccine (LAIV) presented as a nasal spray. The cold-adapted, temperature-sensitive virus strains used in the vaccine replicate in the nasopharynx and induce protective immunity.1

CLINICAL STUDIES

In a meta-analysis of nine randomised clinical trials that included approximately 25,000 children aged 6–71 months and 2000 children aged 6–17 years, LAIV demonstrated efficacy compared with placebo and trivalent inactivated influenza vaccine (TIV).2

Six of the trials compared LAIV with placebo in children aged up to 71 months. In those not previously vaccinated, 2 doses of LAIV had 77% greater efficacy than placebo (p<0.001) in preventing culture-confirmed influenza caused by antigenically similar strains.2 Efficacy of a single dose in previously vaccinated children in year 2 of the studies was 87% compared with placebo (p<0.001).

In one of the six studies, 288 children were randomised in a double-blind fashion to receive either 1 dose of LAIV or placebo and another 1314 were randomised to receive 2 doses of vaccine or placebo approximately 60 days apart. LAIV reduced the occurrence of culture-confirmed influenza with 89% efficacy after a single dose and 94% efficacy after 2 doses. Influenza was milder in the vaccine groups than in the placebo groups (febrile in 57% vs 84% of cases; p<0.05). Overall, there were 21% fewer febrile illnesses (p<0.001) among vaccine recipients than among placebo recipients. LAIV was associated with rhinorrhoea/nasal congestion, fever and decreased activity, although fever was short-lived.3

The other three trials in the meta-analysis compared LAIV with TIV.2 In one double-blind study, children aged up to 59 months (n=7852) received a single dose of vaccine if they had previously been vaccinated and 2 doses if they had not. There were 54.9% fewer cases of culture-confirmed influenza in the group that received LAIV than in the TIV group (p<0.001).4

The second study (n=2187) compared the 2 vaccines in previously unvaccinated children aged up to 71 months with a history of recurrent respiratory tract infections. After 2 doses of vaccine, there were 52.7% fewer cases of influenza in the LAIV group than in the TIV group.5

The third study enrolled older children with asthma, who were randomised to receive a single dose of LAIV (n=1114) or TIV (n=1115). The incidence of community-acquired culture-confirmed influenza illness in the 2 groups was 4.1% and 6.2%, respectively.6

Overall, in these three trials, vaccine-naïve children who received 2 doses of LAIV experienced 46% fewer cases of antigenically similar influenza than those who received 2 doses of TIV. Previously vaccinated older children who received 1 LAIV dose experienced 35% fewer cases of influenza than those given a single dose of TIV.2

Fluenz was studied in children aged from six months but the vaccine is only licensed for use from 2 years of age. In previously unvaccinated children, wheezing was more common with LAIV than TIV, particularly among those aged 6–11 months. Rates of hospitalisation for any cause during the 180 days after vaccination were also increased with LAIV (6.1%) compared with TIV (2.6%) in this age group (p=0.002).4